Upscale impact of mesoscale convective systems and its parameterization in an idealized GCM for an MJO analog above the Equator

Qiu Yang, Andrew J. Majda, Mitchell W. Moncrieff

Research output: Contribution to journalArticlepeer-review

Abstract

The Madden-Julian oscillation (MJO) typically contains several superclusters and numerous embedded mesoscale convective systems (MCSs). It is hypothesized here that the poorly simulated MJOs in current coarse-resolution global climate models (GCMs) is related to the inadequate treatment of unresolved MCSs. So its parameterization should provide the missing collective effects of MCSs. However, a satisfactory understanding of the upscale impact of MCSs on the MJO is still lacking. A simple two-dimensional multicloud model is used as an idealized GCM with clear deficiencies. Eddy transfer of momentum and temperature by the MCSs, predicted by the mesoscale equatorial synoptic dynamics (MESD) model, is added to this idealized GCM. The upscale impact of westward-moving MCSs promotes eastward propagation of the MJO analog, consistent with the theoretical prediction of the MESD model. Furthermore, the upscale impact of upshearmoving MCSs significantly intensifies the westerly wind burst because of two-way feedback between easterly vertical shear and eddy momentum transfer with low-level eastward momentum forcing. Finally, a basic parameterization of the upscale impact of upshear-moving MCSs modulated by deep heating excess and vertical shear strength significantly improves key features of the MJO analog in the idealizedGCMwith clear deficiencies. A three-way interaction mechanism between the MJO analog, parameterized upscale impact of MCSs, and background vertical shear is identified.

Original languageEnglish (US)
Pages (from-to)865-892
Number of pages28
JournalJournal of the Atmospheric Sciences
Volume76
Issue number3
DOIs
StatePublished - Mar 1 2019

Keywords

  • Convection
  • General circulation models
  • Madden-Julian oscillation
  • Mesoscale systems
  • Parameterization
  • Wind shear

ASJC Scopus subject areas

  • Atmospheric Science

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